I am looking to install one of the MRCool DIY mini split in my garage.

I currently have a 30amp 240v break and have run 10 gauge wire to a 20amp receptacle for my air compressor.

Can I just use some wire connectors to splice in the box and add pigtails for my 20amp plug, then Come out of top of the box, drill through the wall and install my disconnect outside? I found some WAGO brand “lever nut” connectors, those good?

How is the inside unit powered? In the instructions it mentions an “air brake switch” that looks like the internal unit is connected to but I can’t find what amps or voltage that runs on.

Thank you

  • 1
    What breaker and wire size does the unit itself require? Commented May 8, 2023 at 11:35
  • Strange. I looked at an installation guide for a MrCool mini-split i happened to have from a couple of years ago, and I can't find anything in there about power needs for the inside unit.
    – SteveSh
    Commented May 8, 2023 at 13:17
  • 1
    Not strange at all. For every mini-split I've looked at in that level of detail, the inside units are powered from the outside unit. Thus the house power connects only to the outside unit. There might be some weird outliers, but that's what I've seen as "normal."
    – Ecnerwal
    Commented May 8, 2023 at 14:07
  • 1
    The outdoor unit will be labeled as to "minimum circuit ampacity" and "maximum overcurrent protection." Those are manufacturer requirements, chosen during the UL testing of the device, and electrical code requires those to be met. On the other hand, the use of a 20A receptacle protected by a 30A breaker violates electrical code. It may be possible that you could install a 30A receptacle and use the one circuit for both devices, but we'll need to know more about the labeled requirements for both machines.
    – Greg Hill
    Commented May 8, 2023 at 15:05
  • What do the instructions say?
    – FreeMan
    Commented May 8, 2023 at 17:10

2 Answers 2


You need to install and wire the equipment according to the labeling and instructions. I'm not harshing on your asking a question, but note that that the following (and thus the reading) is a Code requirement.

There is already a harness of control wires running between the outdoor and indoor unit(s). The interior unit powers nothing but a fan and some LEDs, so most mini-split installations simply throw fan power into that bundle. Thus it is powered from the outdoor unit.

20A receptacles on 30A breakers

That's a no-go. The receptacle size must match the breaker size exactly for 20A, 30A and 50A breakers. 15A receptacles on 20A circuits are an exception, not a rule.

It's perfectly fine to use larger wire than is required, so the #10 is all good.

Further, the mini-split instructions are probably going to require a dedicated circuit. And are probably going to require it be hard-wired.

A disconnect near the A/C.

Code requires a disconnect switch near the unit - as in line-of-sight near, not "other side of wall" near.

Instructions will also (most likely) specify a hard-wired connection with a disconnect.

Now, 'ratchet freak' suggesed a subpanel to split the 30A into dual 20A circuits (or 20A and 15A depending on the needs of the MrCool). I totally agree. Note that a subpanel qualifies as a disconnect, so if the subpanel is placed outside near the unit, and feeds the compressor outlet back inside, we just crossed off the disconnect requirement :) "That was easy"

A 120V outlet is required within 25' of the unit

That is so the maintainer can plug in their vacuum pump. It is NOT required to be dedicated for the mini-split, it can be a general-use outlet. Yes, I know the MrCool unit is DIY for initial installation, but it might need servicing later by a pro certified for handling refrigerants. It's not just the certification, it's the required recovery equipment to prevent damage to the atmosphere, and the supply chain to recycle or destroy that refrigerant.

You cannot get 120V from a 240V circuit that you ran with /2 cable. (however if you ran /3 cable and you take it to a subpanel, you can stick a 120V breaker in the subpanel). Feel free to Extend some other shop circuit if needed.

  • I'm my case, an existing outdoor outlet covered that last requirement.
    – keshlam
    Commented May 8, 2023 at 20:10
  • If I put the sub panel outside: 30amp breaker, 10 gauge wire, out the wall, into sub panel, then dual 20 amp breakers, can I send the wire back inside for my air compressor?
    – user903805
    Commented May 9, 2023 at 16:36
  • @user903805 Yeah, that's fine. Commented May 9, 2023 at 19:03
  • I was looking tonight at a unit with a 24k BTU compared to the 18k than I was originally thinking and When checking the 24k manual it says: MCA:22 amps, MOP:35 amps. Minimum wire gauge for power cables: 8 min, 6 preferred. I’m guessing that means I have to run 8 gauge wire off a 40amp main breaker with a 35 amp breaker in the subpanel because the 10 gauge wire and 30amp I have now is below MOP?
    – user903805
    Commented May 10, 2023 at 0:42

HVAC equipment really likes being on a dedicated circuit as the compressor runs close to the cap of the circuit they are rated for. Most will require one, that includes a dedicated breaker.

What you can do is put in a mini subpanel that will split out the 30A circuit into 2 20A circuits, one to the receptacle and one to the outside unit (or a 30A for the outside unit and a 20A for the receptacle as needed). If you end up getting nuisance trips on the 30A breaker you can use a current sensor to lock out the compressor when the HVAC is drawing a lot of power.

How the inside unit is powered depends on the make and model. Many modern units run power and com wire from the outside unit to the inside unit alongside the refrigeration lines, other models will require an (likely 120V) outlet to power the inside unit and then run a low voltage com line between the units, some have the communication be wireless and only need an outlet at the inside unit. Check the manual.

  • I get the sub panel but can I just not run the compressor when I run the mini split and turn off the mini split when I run the compressor? I run the compressor honestly once a month if that. Id hate to do all the drywall cutting and additional costs for the sub panel and breakers
    – user903805
    Commented May 8, 2023 at 12:34
  • You can find surface mount subpanels especially in the 4-space class that you will need. And yeah you can use a manual select instead of an automatic lockout. Commented May 8, 2023 at 13:36
  • @user903805 - Regions vary but there are two good reasons not run the compressor and mini split on the same circuit: code violation and your home owner's insurance. Commented May 8, 2023 at 17:40
  • @user903805 you 'can' in that it may technically work. You can't however in that code is going to require individual circuits here.
    – KMJ
    Commented May 8, 2023 at 21:49

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